pixman-renderer: implement surface scaling and cropping

The pixman renderer doesn't use the weston_surface_to_buffer*
functions to alter coordinates depending on buffer transformation,
buffer scaling, and surface scaler (wl_surface_scaler).
pixman_transform_scale() is used instead to perform said
transformations without having to modify each coordinate.

src/pixman-renderer.c

@@ -256,9 +256,31 @@ repaint_region(struct weston_view *ev, struct weston_output *output,
 					   pixman_double_to_fixed ((double)-ev->geometry.y));
 	}
 
+	if (ev->surface->buffer_viewport.scaler_set) {
+		double scaler_x, scaler_y, scaler_width, scaler_height;
+		double ratio_x, ratio_y;
 
-	fw = pixman_int_to_fixed(ev->surface->width);
-	fh = pixman_int_to_fixed(ev->surface->height);
+		scaler_x = wl_fixed_to_double(ev->surface->buffer_viewport.src_x);
+		scaler_y = wl_fixed_to_double(ev->surface->buffer_viewport.src_y);
+		scaler_width = wl_fixed_to_double(ev->surface->buffer_viewport.src_width);
+		scaler_height = wl_fixed_to_double(ev->surface->buffer_viewport.src_height);
+
+		ratio_x = scaler_width / ev->surface->buffer_viewport.dst_width;
+		ratio_y = scaler_height / ev->surface->buffer_viewport.dst_height;
+
+		pixman_transform_scale(&transform, NULL,
+				       pixman_double_to_fixed(ratio_x),
+				       pixman_double_to_fixed(ratio_y));
+		pixman_transform_translate(&transform, NULL, pixman_double_to_fixed(scaler_x),
+							     pixman_double_to_fixed(scaler_y));
+	}
+
+	pixman_transform_scale(&transform, NULL,
+			       pixman_double_to_fixed(ev->surface->buffer_viewport.scale),
+			       pixman_double_to_fixed(ev->surface->buffer_viewport.scale));
+
+	fw = pixman_int_to_fixed(pixman_image_get_width(ps->image));
+	fh = pixman_int_to_fixed(pixman_image_get_height(ps->image));
 
 	switch (ev->surface->buffer_viewport.transform) {
 	case WL_OUTPUT_TRANSFORM_FLIPPED:
@@ -294,10 +316,6 @@ repaint_region(struct weston_view *ev, struct weston_output *output,
 		break;
 	}
 
-	pixman_transform_scale(&transform, NULL,
-			       pixman_double_to_fixed ((double)ev->surface->buffer_viewport.scale),
-			       pixman_double_to_fixed ((double)ev->surface->buffer_viewport.scale));
-
 	pixman_image_set_transform(ps->image, &transform);
 
 	if (ev->transform.enabled || output->current_scale != ev->surface->buffer_viewport.scale)